The present invention relates to an electronic control apparatus including a plurality of power source circuits which constitute a plurality of kinds of power sources.
In recent years, higher integration and higher processing rate of ICs are rapidly progressing, and thereby a power source voltage used is further lowered. However, in the case of a product under the severe noise environment such as in an automobile, it is impossible to use a lower power source voltage for peripheral circuits from a viewpoint of noise margin.
Therefore, a dual power source circuit that realizes both higher integration density and noise margin is often used to operate the peripheral circuits with a higher voltage and a CPU or the like with a lower voltage. Moreover, a power source line is individually provided for the circuits such as an oscillation circuit or the like which requires reduction of noise due to radiated electromagnetic wave and an A/D converter circuit which requires higher accuracy.
When a one-chip microcomputer having such a plurality of power source lines is used, operation of the microcomputer cannot be ensured during an abnormality of the power source line and operation of the microcomputer becomes unstable when the power source is turned on or turned off. Therefore, when such a one-chip microcomputer is used in ABS (Anti-lock Brake System), it is probable that the brake function will be lessened.